1. Field of the Invention
The present invention relates to a backlight module and a reflective cover used in the backlight module and, more particularly, to a backlight module for providing a planar illuminating light to a liquid crystal display (LCD) panel.
2. Discussion of the Related Art
In recent years, LCD devices, such as liquid crystal monitors, and liquid crystal TVs have become widely used. A typical LCD device includes an LCD panel and a backlight module positioned under the LCD panel for supplying light thereto.
Referring to FIG. 6, a typical backlight module 10 includes two point light sources 11, a light guide plate (LGP) 12, a reflective sheet 13, a diffusing sheet 14, and two light condensers 15. The two point light sources 11 are generally light-emitting diodes (LEDs). The LGP 12 includes a light incidence surface 121, a light-emitting surface 122 connecting with the light incidence surface 121, and a bottom surface 123 facing the light-emitting surface 122. The two point light sources 11 are placed at the light incidence surface 121 of the LGP 12. The reflective sheet 13, the LGP 12, the diffusing sheet 14, and the two light condensers 15 are arranged in that order.
In operation, the point light source 11 emits light. The light is transmitted into the LGP 12 through the light incidence surface 121. The LGP 12 is used for guiding the light to exit from the light-emitting surface 122 thereof. The reflective sheet 13 reflects a portion of the light exiting from the bottom surface 123 of the LGP 12. The reflected portion of the light is thus redirected to exit from the light-emitting surface 122. The light exiting from the light-emitting surface 122 passes through the diffusing sheet 14 and the two light condensers 15 in sequence. The two light condensers 15 are configured for collimating diffused light emitting from the diffusing sheet 14. Thus, the backlight module 10 can generate a planar illuminating light with a high brightness.
Referring to FIG. 7, each point light source 11 has a limited illuminating space. Light beam L1 in the center of the illuminating space is substantially perpendicular to the light incidence surface 121, and can exit from a first portion of the light-emitting surface 122 opposite to the point light source 11. Light beam L2 in the border of the illuminating space is not perpendicular to the light incidence surface 121, and can exit from a second portion of the light-emitting surface 122 opposite to a position between the two point light sources 11. There is a dark region 124 (defined by a broken line in FIG. 7) to which the light emitting from the two point light sources 11 hardly reaches. The dark region 124 is displayed on the light-emitting surface 122, thus it can be seen that the backlight module 10 does not provide uniform brightness.
What is needed, therefore, is a backlight module that can provide uniform brightness.